The invention relates to an automatic clutch control system which automatically control the coupling of a driven shaft to a drive shaft in a clutch mounted on an automobile in accordance with a decision rendered by an electronic unit.
In a conventional automatic clutch arrangement, the degree of engagement of the clutch is determined in analog manner in accordance with the number of revolutions of an engine only upon starting, but an on-and-off control of the clutch is employed during a subsequent shift operation which occurs after the vehicle has been started. Consequently, if there is a difference between the number of revolutions of the engine and the number of revolutions of the clutch to cause a sudden complete engagement of the clutch, a driver of the vehicle may experience an uncomfortable shock. To alleviate this, a variable rate is employed for engagement of the clutch, since the magnitude of a negative pressure prevailing in an engine manifold allows the differential number of revolutions to be known. However, the technique suffers from a disadvantage that an accurate control cannot be achieved since the magnitude of the negative pressure changes from vehicle to vehicle and because a long time delay is involved.
To accomodate for this difficulty, there has been proposed to achieve an accurate engagement of a clutch without experiencing a shock in a clutch arrangement in which a clutch transmits rotating power to an output shaft. The arrangement comprises a power sensor for detecting the number of revolutions of the output shaft, a clutch sensor for detecting the number of revolutions of the clutch, a comparator for determining the relative magnitude of the number of revolutions of the both sensors, a parameter of follow-up control responsive to an output from the comparator to activate the clutch for engagement as the number of revolutions of the output shaft increases whenever the number of revolutions of the output shaft is higher than that of the clutch, and an automatic engaging circuit responsive to an output from the comparator and operating whenever the number of revolutions of the clutch is higher to deactuate the follow-up control and to terminate automatically the engagement of the clutch within a given time interval. In this manner, the relative magnitude of the number of revolutions of the engine and the clutch is determined in an electrical manner, and whenever the number of revolutions of the engine is higher than that of the clutch, an engagement of the clutch occurs in response to the number of revolutions of the engine while whenever the number of revolutions of the engine is lower than that of the clutch, an engagement of the clutch takes place in accordance with a difference therebetween. (See Japanese Patent Publication No. 26,020/1978, filed Mar. 26, 1971 and published Jul. 31, 1978). In other words, the rotational speed of the engine is chosen as a main variable while a differential speed between the output shaft of the clutch (driven shaft) and the output shaft of the engine (the clutch drive shaft) is chosen as a parameter for controlling the clutch coupling power. To summarize, in a mode in which the vehicle is driven for running under the engine power, the clutch coupling power is controlled in a manner corresponding to the rotational speed of the engine while in an engine brake mode, the clutch coupling power is controlled as a particular function of time.
In either instance, the engagement of the clutch is initiated on the conditions that the shift lever position is either in its drive D or reverse R position and the rotational speed of the engine is equal to or greater than a given value. The degree of engagement of the clutch is controlled in accordance with the rotational speed of the engine. One of the problems experienced in such automatic control of the clutch described relates to a frequent switching of the shift lever position between its drive D and reverse R position when the vehicle gets into sand or mire or when the vehicle drives past an obstacle on the road or makes a turn in a narrow road. In such instance, the shift lever may assume its reverse R position to initiate the engagement of the clutch while the driven shaft of the clutch is still rotating in the forward direction. Alternatively, the shift lever may assume its drive D position to initiate the clutch engagement while the driven shaft is still rotating in the rearward direction. A loading on the engine increases in these instances, causing shocks to the vehicle or an engine stop.